Department of Condensed Matter, School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel.
Center for Physics and Chemistry of Living Systems, Tel-Aviv University, Tel Aviv 69978, Israel.
Proc Natl Acad Sci U S A. 2022 Jul 12;119(28):e2200028119. doi: 10.1073/pnas.2200028119. Epub 2022 Jul 6.
Crumpling an ordinary thin sheet transforms it into a structure with unusual mechanical behaviors, such as enhanced rigidity, emission of crackling noise, slow relaxations, and memory retention. A central challenge in explaining these behaviors lies in understanding the contribution of the complex geometry of the sheet. Here we combine cyclic driving protocols and three-dimensional (3D) imaging to correlate the global mechanical response and the underlying geometric transformations in unfolded crumpled sheets. We find that their response to cyclic strain is intermittent, hysteretic, and encodes a memory of the largest applied compression. Using 3D imaging we show that these behaviors emerge due to an interplay between localized and interacting geometric instabilities in the sheet. A simple model confirms that these minimal ingredients are sufficient to explain the observed behaviors. Finally, we show that after training, multiple memories can be encoded, a phenomenon known as return point memory. Our study lays the foundation for understanding the complex mechanics of crumpled sheets and presents an experimental and theoretical framework for the study of memory formation in systems of interacting instabilities.
将普通薄纸揉成一团会使其变成具有特殊机械性能的结构，例如增强的刚性、噼啪作响的噪声、缓慢的松弛和记忆保持。解释这些行为的一个核心挑战在于理解薄片复杂几何形状的贡献。在这里，我们结合循环驱动协议和三维（3D）成像，关联展开褶皱薄片的全局机械响应和潜在的几何变形。我们发现它们对循环应变的响应是间歇性的、滞后的，并编码了最大应用压缩的记忆。使用 3D 成像，我们表明这些行为是由于薄片中的局部和相互作用的几何不稳定性之间的相互作用而产生的。一个简单的模型证实，这些最小的成分足以解释观察到的行为。最后，我们表明，经过训练，可以编码多个记忆，这是一种称为返回点记忆的现象。我们的研究为理解褶皱薄片的复杂力学奠定了基础，并为研究相互作用不稳定性系统中的记忆形成提供了实验和理论框架。
